At bcae1.com they had a power/voltage loss demp calculator in the wires section.
I simply put the length of 0 guage cable from battery to amp and 0 guage battery negative to chassis and 0 guage amp ground to chassis. typed in 1687 watts (cuz thats what the Opti2000d does at 1 ohm).
I came up with 1000w RMS at just over half volume with a .4 voltage drop...on the calc it says I could max the volume out and I still would only have a .5v drop at worse.